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Merge pull request #3501 from iluxonchik/refactor-kotlin-examples
[Kotlin/EN] Refactor kotlin examples
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3844aa7c33
@ -109,7 +109,7 @@ fun helloWorld(val name : String) {
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/*
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When a function consists of a single expression then the curly brackets can
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be omitted. The body is specified after a = symbol.
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be omitted. The body is specified after the = symbol.
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*/
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fun odd(x: Int): Boolean = x % 2 == 1
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println(odd(6)) // => false
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@ -306,7 +306,7 @@ fun helloWorld(val name : String) {
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println(result)
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/*
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We can check if an object is a particular type by using the "is" operator.
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We can check if an object is of a particular type by using the "is" operator.
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If an object passes a type check then it can be used as that type without
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explicitly casting it.
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*/
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@ -346,11 +346,6 @@ fun helloWorld(val name : String) {
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return this.filter {it != c}
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}
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println("Hello, world!".remove('l')) // => Heo, word!
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println(EnumExample.A) // => A
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println(ObjectExample.hello()) // => hello
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testOperator()
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}
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// Enum classes are similar to Java enum types.
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@ -358,6 +353,8 @@ enum class EnumExample {
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A, B, C
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}
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fun printEnum() = println(EnumExample.A) // => A
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/*
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The "object" keyword can be used to create singleton objects.
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We cannot instantiate it but we can refer to its unique instance by its name.
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@ -367,11 +364,18 @@ object ObjectExample {
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fun hello(): String {
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return "hello"
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}
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override fun toString(): String {
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return "Hello, it's me, ${ObjectExample::class.simpleName}"
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}
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}
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fun useObject() {
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ObjectExample.hello()
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val someRef: Any = ObjectExample // we use objects name just as is
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fun useSingletonObject() {
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println(ObjectExample.hello()) // => hello
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// In Kotlin, "Any" is the root of the class hierarchy, just like "Object" is in Java
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val someRef: Any = ObjectExample
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println(someRef) // => Hello, it's me, ObjectExample
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}
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@ -381,69 +385,54 @@ throws an exception if the value is null.
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var b: String? = "abc"
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val l = b!!.length
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/* You can add many custom operations using symbol like +, to particular instance
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by overloading the built-in kotlin operator, using "operator" keyword
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data class Counter(var value: Int) {
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// overload Counter += Int
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operator fun plusAssign(increment: Int) {
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this.value += increment
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}
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below is the sample class to add some operator, and the most basic example
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*/
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data class SomeClass(var savedValue: Int = 0)
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// overload Counter++ and ++Counter
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operator fun inc() = Counter(value + 1)
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// overload Counter + Counter
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operator fun plus(other: Counter) = Counter(this.value + other.value)
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// overload Counter * Counter
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operator fun times(other: Counter) = Counter(this.value * other.value)
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// overload Counter * Int
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operator fun times(value: Int) = Counter(this.value * value)
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// overload Counter in Counter
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operator fun contains(other: Counter) = other.value == this.value
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// overload Counter[Int] = Int
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operator fun set(index: Int, value: Int) {
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this.value = index + value
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}
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// overload Counter instance invocation
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operator fun invoke() = println("The value of the counter is $value")
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// instance += valueToAdd
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operator fun SomeClass.plusAssign(valueToAdd: Int) {
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this.savedValue += valueToAdd
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}
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/* You can also overload operators through an extension methods */
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// overload -Counter
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operator fun Counter.unaryMinus() = Counter(-this.value)
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// -instance
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operator fun SomeClass.unaryMinus() = SomeClass(-this.savedValue)
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// ++instance or instance++
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operator fun SomeClass.inc() = SomeClass(this.savedValue + 1)
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// instance * other
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operator fun SomeClass.times(other: SomeClass) =
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SomeClass(this.savedValue * other.savedValue)
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// an overload for multiply
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operator fun SomeClass.times(value: Int) = SomeClass(this.savedValue * value)
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// other in instance
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operator fun SomeClass.contains(other: SomeClass) =
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other.savedValue == this.savedValue
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// instance[dummyIndex] = valueToSet
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operator fun SomeClass.set(dummyIndex: Int, valueToSet: Int) {
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this.savedValue = valueToSet + dummyIndex
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}
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// instance()
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operator fun SomeClass.invoke() {
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println("instance invoked by invoker")
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}
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/* return type must be Integer,
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so that, it can be translated to "returned value" compareTo 0
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for equality (==,!=) using operator will violates overloading equals function,
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since it is already defined in Any class
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*/
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operator fun SomeClass.compareTo(other: SomeClass) =
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this.savedValue - other.savedValue
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fun testOperator() {
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var x = SomeClass(4)
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println(x) // => "SomeClass(savedValue=4)"
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x += 10
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println(x) // => "SomeClass(savedValue=14)"
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println(-x) // => "SomeClass(savedValue=-14)"
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println(++x) // => "SomeClass(savedValue=15)"
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println(x * SomeClass(3)) // => "SomeClass(savedValue=45)"
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println(x * 2) // => "SomeClass(savedValue=30)"
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println(SomeClass(15) in x) // => true
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x[2] = 10
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println(x) // => "SomeClass(savedValue=12)"
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x() // => "instance invoked by invoker"
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println(x >= 15) // => false
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fun operatorOverloadingDemo() {
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var counter1 = Counter(0)
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var counter2 = Counter(5)
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counter1 += 7
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println(counter1) // => Counter(value=7)
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println(counter1 + counter2) // => Counter(value=12)
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println(counter1 * counter2) // => Counter(value=35)
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println(counter2 * 2) // => Counter(value=10)
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println(counter1 in Counter(5)) // => false
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println(counter1 in Counter(7)) // => true
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counter1[26] = 10
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println(counter1) // => Counter(value=36)
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counter1() // => The value of the counter is 36
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println(-counter2) // => Counter(value=-5)
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}
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```
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